How To Increase Horsepower - You Can Build It!

By doing your homework, you can breathe hundreds of horsepower to life with your own two hands.

No one is born knowing how to file down rings or torque down main caps, so there’s nothing wrong with being an engine-building virgin. Who cares if your more experienced gearhead buddies might bust your chops about it? We all have to start somewhere, and with enough research and practice, you’ll be able to smoke those fools with a kickin’ engine combination that you built with your own two hands. Perhaps the greatest attribute of Chevy small- and big-blocks isn’t so much their prolific horsepower potential, but rather how easy and affordable they are for anyone to build right in your own garage. As hot rodders, the urge to plan and execute your first engine build is only natural; however, knowledge is the best defense against making costly mistakes. Fortunately, help is only a couple of paragraphs away.

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In reality, explaining how to build an engine one step at a time is beyond the scope of any single magazine story. Instead, we’ll walk you through the logistics process that every engine build must go through before a single wrench is turned. The first step involves establishing a budget, then determining horsepower and streetability targets. From there, it’s a matter of deciding upon a cubic-inch tally that best suits your needs, then selecting a block, rotating assembly, camshaft, valvetrain, and cylinder heads to make it all happen. Then comes the fun part: turning a pile of parts into a running engine. As anyone who has ever built a motor will attest, there’s nothing like cracking the throttle on an engine you built yourself for the very first time.

Instead of masquerading as engine builders, we acknowledged our status as scribes, and tapped into the expertise of Smeding Performance. The company has been building turnkey crate motors for over 20 years, and boasts an impressive product line ranging from 360hp small-blocks to 900hp-blown big-blocks. Smeding Performance builds more engines in one week than most hot rodders build in their life, and as such, it has a wealth of insight and expert tips in its data bank to share with enthusiasts.

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Keeping it Practical

Race motors are interesting specimens of engineering that boast insane horsepower. The only thing more insane is how much they cost to build, and the amount of maintenance they require. Sure, it’s easy to be wowed by the 11,000-plus rpm that NHRA Pro Stock engines turn while producing nearly 3 hp per cubic inch. However, the only reason teams must abuse their motors so thoroughly by turning so many rpm is due to rules and restrictions that limit maximum displacement. The good news for street cars is that there is no sanctioning body that limits the number of cubic inches you can pack into your street machine. Since larger motors produce more torque, and horsepower is nothing more than torque multiplied by rpm, they can make the same horsepower as smaller displacement motors without having to turn as many rpm. The net effect of keeping the rpm down is vastly improved valvetrain reliability, smoother idle quality, and the ability to run taller gearing for more relaxed freeway cruising and increases in fuel mileage. Likewise, turning fewer rpm means that you can get by with a less aggressive camshaft, which substantially improves driveability in addition to fattening up low and midrange torque. Consequently, if you use the largest cubic-inch short-block that you can afford as the foundation for your engine build, it’s hard to go wrong. “Our goal is to design a motor to be as efficient as possible for the rpm range we want to run it in, then to use the best cylinder heads available,” Ben Smeding explains. “That way, you don’t need to run a big cam, which makes an engine combination much more streetable.”

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How To Increase Horsepower - You Can Build It!

Whether they’re from GMPP or Dart, Smeding uses brand-new blocks exclusively in all its crate engine packages. Although used cores can serve as great foundations for performance motors, using new blocks eliminates the potential for excessive cylinder bore and main cap wear, rust in the water jackets, and stripped boltholes.

Whether they’re from GMPP or Dart, Smeding uses brand-new blocks exclusively in all its crate engine packages. Although used cores can serve as great foundations for performance motors, using new blocks eliminates the potential for excessive cylinder bore and main cap wear, rust in the water jackets, and stripped boltholes.

The last thing you want to do is install a high-dollar rotating assembly and valvetrain into a block with poor machine work. Even if you’re on a limited budget, machine work is one area where it doesn’t pay to skimp. Smeding installs torque plates on top of the block during the honing process to simulate the clamping loads of the cylinder heads. After machining is complete, the block is hot-tanked.

Here’s just one example of where an experienced engine shop is priceless. The Fed’s push to reduce vehicle emissions has resulted in motor oils in which critical lubrication-enhancing additives have been eliminated. Smeding noticed excessive valvetrain wear on its flat-tappet cam motors, and came up with a simple yet ingenious solution. By notching a 0.012-inch groove into the bottom side of each lifter bore, Smeding is able to dramatically improve oil flow and reduce lifter wear.

Replacing the cam bearings is standard procedure in any engine build. The process involves tapping the bearings into the cam tunnel with a special installation tool and a hammer. Care must be taken to ensure that the oiling holes in the cam tunnel align perfectly with the holes in the bearings. This is particularly important on production blocks that lubricate the cam bearings before the crank and rods. Most machine shops will charge about $30 to install new bearings.

After applying sealant around the perimeter of the freeze plugs, the easiest way to install them is with a socket and hammer. Smeding uses a socket that’s slightly smaller than the lip of the freeze plug and taps it into place.

The excitement and rush to put a short-block together can make it easy to overlook the little things. Both Gen I small- and big-blocks have coolant drains along the sides of the block, and oil ports near the filter boss. They must be closed off with pipe plugs to prevent a big ugly leak.

During the balancing process, bob weights are bolted to the crankshaft. They’re equal in mass to 100 percent of the rotating weight (big rod ends, rod bearings), and 50 percent of the reciprocating weight (pistons, pins, locks, small rod ends). With today’s lightweight rods and pistons, material is typically removed from the crank counterweights, although heavy metal is sometimes added in extremely long-stroke cranks that have small counterweights. Since a crankshaft acts as a lever, the farther away from the crank centerline the weight is removed, the greater affect it has on balance.

After the crank has been balanced, Smeding polishes all of the main and rod journals. This removes all surface scratches prior to assembly.

With the machine work complete, it’s time to start assembling the short-block. The main bearings have tabs that help locate them into a slot in the block. The block half of the bearing has an oiling hole, while the main cap side does not.

Once the main bearings have been installed, the main caps must be torqued down before checking bearing clearance. Using a dial bore gauge to measure the bearing inside diameter, then comparing it to the diameter of the main journals measured with a micrometer will give a good indication of the bearing clearance. As long as a block is in good shape, or has been align-honed, variations from cap to cap should be minimal, and can be adjusted if necessary with undersized bearings. For street engines, 0.0025- to 0.0035-inch clearance is typical, while race motors may have 0.0035 to 0.0040 inch of clearance.

It’s much easier to install the camshaft before the crankshaft has been bolted down. Spreading assembly lube around the cam journals and lobes is common practice, but Smeding prefers installing it dry. Once the cam is 3 inches from being fully installed, Smeding applies lube before sliding it in the rest of the way.

After the crank has been positioned into the block, the main caps can be installed. Numbers and arrows cast into the caps tell you where they go. The arrows should point toward the front of the motor, and the caps are numbered 1-5, from front to back. It’s best to seat the caps onto the block with a mallet instead of forcing them down with bolts, since the latter can crack the cap. With four-bolt caps, the inner bolts should be torqued down first, followed by the outer bolts.

With the main caps torqued down, crank endplay can now be checked. This is done by wedging a pry bar between the block bulkhead and the crank counterweight, and moving the crank back and forth. Using a dial indicator on the crank snout, endplay should check in at 0.005 to 0.008 inch.

Most aftermarket rings must be filed down to achieve the proper gap. Electric filers make the job easier, but manual filers work great as well. For naturally aspirated street/strip engines, a gap of 0.0045 inch for every inch of bore is recommended for the top ring, and 0.0055 inch for every inch of bore on the second ring. That equates to a 0.018- and 0.022-inch gap on the top and second rings, respectively, on a 4-inch bore motor. For nitrous and forced-induction applications, a larger 0.0050-inch gap per inch of bore is recommended. These are good rules of thumb, but different piston manufacturers have different guidelines, so it doesn’t hurt to check with them directly for their recommended gap specs.

The proper way to install piston rings is with a ring spreading tool. Spiraling the rings on by hand distorts them, and compromises their ability to seal the bores. The first and second rings have dimples that help orient them. The dimpled side of the ring should always face upward. The goal is for the chamfered edge of the ring to face upward on the top ring, and downward on the second ring. Conversely, the oil rings can be installed in either direction.

Before hanging the rods on the pistons, it’s a good idea to make sure the piston valve reliefs are oriented correctly for the cylinder in which they will be installed. The big ends of rods are chamfered on both sides, but the side with larger chamfer must face the crank counterweight.

After sliding the wristpin through the piston and rod, snap ring pliers are required to secure everything in place. With piston pins that use spiral locks, the locks must be unwound, then slowly spiraled into position with a small flathead screwdriver.

As the pistons and rods travel up toward TDC in a stroker motor, it’s not uncommon for the rods to hit the cam. To prevent this, many aftermarket rods have profiled shoulders that offer additional clearance.

As with the main bearings, rod bearings also have tabs that help locate them in the big end. When installed correctly, both the tabs should be on the same side of the rod. For street/strip motors 0.0025 to 0.0035 inch of rod clearance is common.

Prior to assembly, Smeding thoroughly cleans all wear surfaces and wipes them down with WD-40. When installing the rotating hardware, assembly lube is used liberally on the main and rod journals. Oil is then squirted down each bore before installing the pistons.

Next, using a ring compressor and the small end of a mallet, the piston and rod assembly are installed into each bore. Smeding holds the rod end of the assembly by hand to prevent it from inadvertently gouging the cylinder wall.

Rod bolts can either be torqued down to spec, or installed using a bolt stretch gauge. This is also a good time to check rod side clearance with a feeler gauged. Anywhere from 0.010 to 0.015 inch is acceptable for a street/strip engine.

When installing the oil pump on the Number 5 main cap, it may be necessary to enlarge the locating holes slightly to get them to slide over the dowels. It’s important to pay close attention to the pump driveshaft to make sure that the tang slides into the oil pump groove.

The crank gear has a slot that locates it onto the crankshaft snout keyway. Since it’s an interference fit, beating the gear onto the snout with a hammer isn’t advisable. Smeding uses a brass sleeve and hammer to tap the crank gear into place.

With the timing set and cover installed, Smeding mocks the oil pan onto the block without the gasket, then rotates the motor over by hand to check for any potential clearance issues. Eliminating the gasket in this step makes clearance problems more obvious, and therefore easier to detect. Maintaining 0.250 inch of clearance between the oil pump pickup and pan ensures proper oil flow. After the clearance checks out, Smeding lays down RTV on both sides of the gasket around the timing set, then bolts down the pan.

Piston deck height is a measure of how far above or below the top of the piston rests in relation to the deck surface at TDC. It must be measured with a deck clearance gauge to accurately calculate the compression ratio.

Degreeing a cam is a quick way of ensuring that the camshaft is within specification, and phased properly in the motor. Smeding advanced the cam in this 572 by 2 degrees.

At this point, the assembly of the short-block is complete. After installing the lifters and head gaskets, it’s time to move onto the top end.

When installing the cylinder heads, they must be torqued down using a sequence specific to small- or big-blocks. Smeding uses AFR’s 325cc castings on its 572 crate motors, which flow a very impressive 384 cfm. They’re outstanding performers in street/strip applications, whereas anything larger is better suited for higher-rpm applications. On Gen I small-blocks, 200cc and smaller heads generally work very well in mild street/strip combos. Going any bigger in port volume requires a commitment to wind out a motor past 7,000 rpm, or building a 400ci-plus short-block.

After installing the pushrods and rocker, and lashing the valves, Smeding lays down the intake manifold gaskets and a bead of RTV on the front and back of the block, between the heads. Running a bead of RTV around the coolant passages helps seal the cylinder heads as well.

With the hard work out of the way, bolting the Edelbrock Victor Jr. intake and Quick Fuel Technology 950-cfm carb is cake. Smeding rates this beastly 572 at 690 hp and 700 lb-ft of torque. Complete with a three-year, unlimited-mile warranty, it costs a very reasonable $13,000. CHP

Check out this Smeding Performance 572 Crate Motor that kicks out 737hp and 740lb-ft torque. Read more only at www.chevyhiperformance.com, the official website for Chevy High Performance Magazine! » Read More

Check out how much power we get as we test Airflow Research's 235cc cylinder heads on a 400ci Dart Little M block. Only at www.chevyhiperformance.com, the official website for Chevy High Performance Magazine! » Read More